One item preview option and one option that allows players flagged as donator ('1') to access the vendor.
Then make a column in your char or acc db and make it '0' by default. Then just mess around with the donation script to add a '1' in that column if the player donated.
Or just add each item to the multivendor menu (additem) then you can have diffrent donator ranks depending on how much they donated for example:
'1' = 10USD
'2' = 20USD
To get item#1 rank '1' is required.
This will require a custom donnor php system, abit to much for a repack?